Method and Composition for Curing Lost Circulation

ABSTRACT

The invention provides a composition made of fibers and a material able to exhibit reverse solubility. The invention preferably is used in a well and as a method to cure lost circulation.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a DIVISIONAL application of U.S. application Ser. No. 13/054605,filed on Mar. 31, 2011 and published on Jul. 28, 2011 as US2011/0183871,the entire content of which is incorporated by reference in itsentirety, which in turn claims the priority and benefit of Europeanpatent application no. 08290781.7, filed on 18 Aug. 2008.

BACKGROUND OF THE INVENTION

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

The present invention broadly relates to well treating. Moreparticularly the invention relates to a composition designed to curelost circulation in general, including cementing, drilling, completionand related method for curing lost circulation in a well, such as forinstance oil or gas well.

Cement in oil and gas wells is placed in the annular gap between thedrilled formation and the steel casing. Its primary main function is toprevent any fluid communication between the drilled formations toprovide long-term zonal isolation. Lost circulation is a common problemencountered during drilling and cementing, which accounts forsignificant amount of non-producing time. Many prior art's products andtechniques have been developed to solve this problem. One of the mostpracticed techniques is to add conventional loss circulation material(LCM) to the drilling fluids, cement slurries or pills. Recently, theuse of well-defined fibers has become popular due to its superiorperformance, and has been used successfully with drilling fluids andcement slurries. Patent applications WO2004101704, US20060157244 andpatents U.S. Pat. No. 5,782,300, EP1284248 disclose such systems.Combination with other granular material was also tested (reference canbe found in scientific papers from Society of Petroleum Engineers,SPE73791 and SPE54323).

Pills, fibrous materials and conventional LCM are widely used to curelost circulation. They often are used together to improve the overallefficiency. Higher solid or fiber contents often times perform better insealing the lost zones. However, the concentrations for these addedmaterials must not exceed the maximum values governed by operations andequipments. For example, high concentrations of fiber will render thetreatment system unpumpable and risk choking the pumps and plugging thedownhole assemblies. As such, there is a need to solve this dilemma andto improve the performance of fibers and LCM without incorporating moresolid materials. For this reason, it is important to develop a newtechnology with improved fiber performance and excellent losscirculation properties without necessarily increasing fiberconcentration.

SUMMARY OF THE INVENTION

The invention discloses a system for use in a well, comprising fibersand a material able to exhibit reverse solubility. The material can be areverse-water-solubility polymer. Preferably, the system comprisesfibers, and a material able to exhibit reverse solubility and a secondmaterial able to stick fibers in a network when activated. By activationit is meant that the material which has no or little adhesive propertybecomes adhesive when subjected to an activation which can be of anytype as mechanical (stress), chemical (pH) or physical (temperature).Preferably, the material is activated by change of temperature and/orpH.

The fibers can be: metallic amorphous fibers, metallic non-amorphousfibers, glass fibers, carbon fibers, polymeric fiber (polypropylene,novoloid, glass, polylactic resin) or a mixture thereof. The system ofthe invention can be used with a base fluid made of water preferablywith a hydraulic cement or with a base fluid made of oil.

According to another aspect of the invention a method for treatment in awell is disclosed, the method comprising the steps of: pumping in thewell a composition made of fibers and a material able to exhibit reversesolubility; and allowing the composition to form the network in the wellby activating the sticking. The method is preferably used with systemsas disclosed previously.

The method applies advantageously to cure lost circulation of a zone inthe well, so the method comprises further the step of drilling the welland the composition forms the network in the vicinity of the zone.

The method can be used with a hydraulic cement added to the composition,or with the composition used as a drilling fluid for the drilling step,or as a spacer. Drilling fluid can be oil-based mud or water-based mud.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the present invention can be understood with theappended drawings:

FIG. 1 shows the system according to the invention for the improvedefficiency in terms of plugging the fluid.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any suchactual embodiment, numerous implementation—specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem related and business related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure. In addition, the compositionused/disclosed herein may also comprise some components other than thosecited. In the summary of the invention and this detailed description,each numerical value should be read once as modified by the term “about”(unless already expressly so modified), and then read again as not somodified unless otherwise indicated in context. Also, in the summary ofthe invention and this detailed description, it should be understoodthat a concentration range listed or described as being useful,suitable, or the like, is intended that any and every concentrationwithin the range, including the end points, is to be considered ashaving been stated. For example, “a range of from 1 to 10” is to be readas indicating each and every possible number along the continuum betweenabout 1 and about 10. Thus, even if specific data points within therange, or even no data points within the range, are explicitlyidentified or refer to only a few specific, it is to be understood thatinventors appreciate and understand that any and all data points withinthe range are to be considered to have been specified, and thatinventors possessed knowledge of the entire range and all points withinthe range.

This invention describes the utilization of materials that exhibitreverse solubility; by reverse solubility, it has to be understood inthe present context that the material is completely soluble belowcertain threshold temperatures and then precipitate or phase separatefrom the main fluid systems when surrounding temperatures exceed thethreshold. The thus separated materials can be used to improve solidcontents in-situ and/or provide binding property to agglomerate fibersand LCM together to improve the effectiveness of sealing the lost zone.There are many polymeric materials exhibit reverse solubility or cloudpoints, for example, the EOPO co-polymers.

The RWS (reverse-water-solubility) polymers utilized in the presentinvention contain water-soluble block segments which become less solubleabove the cloud point. Without being bound by any theory, the inventorsbelieve that this occurs because the block segment loses its water ofhydration. Polymers containing poly(oxyalkylene) and/or poly-oxazolinewhich exhibit reverse water solubility can be utilized in the presentinvention. In addition to the poly(oxyalkylene) or poly-oxazoline, thepolymers utilized in the present invention can contain linking groupswhich connect the poly(oxyalkylene) or poly-oxazoline. These linkinggroups include, but are not limited to, polyester, polyamide,polycarbonate, polyacrylate and polyurethane and mixtures thereof. Theresulting polymers can be linear or branched. In a preferred embodiment,the RWS material is chosen from the group consisting of polymerscontaining poly(oxyalkylene) or polyoxazoline and mixtures thereof.

The RWS polymers utilized in the present invention include anyreverse-water-soluble polymer that is at least 1% soluble in water at20° C. and has a cloud point (at 1% actives) that is greater than 20° C.and less than 60° C. Linear or branched poly(oxyethylene) containingpolyurethanes with the above solubility and cloud point properties arepreferred.

An especially useful class of RWS polymers is thepoly(oxyethylene)-poly(oxypropylene) adducts of poly-isocyanates. Thisclass of RWS polymer is represented by formula (I):

wherein R is the aliphatic or aromatic residue of a reactant containing3 or more isocyanate reactive groups; each Z is independently hydrogen,C₁-C₈-alkyl or an additional R group; X is 3 or greater and the sum ofm+n is 6 or greater; with the proviso that there are enoughpoly(oxyethylene) residues to make the polymer soluble at 1% actives inwater at room temperature.

In the instance when Z is an additional R group, thepoly(oxyethylene)/poly(oxypropylene) block segments are, for examplecapped with another polyisocyanate where the additional isocyanategroups are reversibly blocked.

Compounds of formula (I) are obtained by the reaction of apolyisocyanate containing 3 or more—NCO groups per molecule with amono-alcoholic-ether of a polyalkylene glycol (such as the productresulting from the addition of ethylene/oxide and/or propylene oxide toan alcohol).

Examples of reactants containing 3 or more reactive isocyanate groupswhich form the residue R are polyphenylene polyisocyanate andhexamethylene-diisocyanate trimer. Polyphenylene polyisocyanate isrepresented by formula II wherein y is 3 or greater.Hexamethylene-diisocyanate trimer is represented by formula (III):

RWS polymers of formula (I) are preferably those in which x is 3 to 30,m is 0 to 100 and n is 5 to 500. Z is preferably C₁-C₈-alkyl and is mostpreferably butyl.

Poly(oxyethylene)-poly(oxypropylene) adducts of formula (I) wherein Z isbutyl are known as thermosensitizers for aqueous dye dispersions whichthermocoagulate dispersed dye particles to inhibit their migrationduring textile drying operations: Such alkoxylated-polyisocyanates arecommercially available as MODAREZ (Societe' Protex-distributed in the U.S. by Synthron).

The RWS is a trigger for improving sealing/plugging efficiency of lostcirculation systems. This class of material, under formationtemperature, increase solid content and can also work as a binder tofacilitate the formation of agglomerates of LCM solids and/or fibers.This binding property can also improve the mechanical strength of theagglomerates and thus withstand higher differential pressure.

The RWS materials can be dissolved in the base fluids systems, since themajority of them are non-ionic and inert polymers; therefore, we doexpect broad compatibility with existing lost circulation chemistry andsystems.

In a preferred embodiment, the RWS material is used at a concentrationof from 2 to 10% by weight of the base fluid. The based fluid may beindifferently aqueous based or non aqueous based. Preferably, theconcentration in RWS is from 3 to 6 wt %.

Current invention is for use within a well in any type of fluids thatare pumpable. Preferably, the invention can be used in well treatmentsin conjunction with water-based mud, oil-based mud, spacer, or cementslurries . . . The primary application is for curing lost circulation;however the technique can be expanded to other wellbore treatment suchas gravel packing, proppant flowback control, wellbore consolidation andothers. In this way, sticky material facilitates the formation ofimpermeable barriers, which stops fluid from losing into the fracturesor the cracks of formation in interest. To form the impermeable barrier,insoluble solid additives in the wellbore service fluids need tophysically or chemically support each other and adhere to the surface ofthe fractures. By insoluble solid additives it is meant solid additiveswhich remain insoluble at the downhole conditions. The introduction ofthe RWS polymers improves the efficiency of forming the barriers, andalso strengthens the adhesion to the fracture surfaces. Thissubsequently leads to better efficiency in regards to curing lostcirculation.

For instance, fibers are commonly used during the well treatment forsolving the lost circulation problem. Those fibers are generally mineralfibers, as glass fiber, carbon fiber or metallic fiber made of amorphousor non-amorphous metal. Also polymeric fibers can be used.

In another aspect, the system is made of fibers, RWS polymer and amaterial able to stick said fibers in a network when activated. In thebroadest sense, sticky properties could come from the fibers directly orcan be introduced as an additional material. For example, one could usefiber made of or coated with the material that has adhesive propertieswhen activated. Also, in another embodiment, these adhesive materialscan be added and mixed with conventional fibers. Alternatively, thereexists other possible combination, as long as one of the componentspossesses adhesive properties.

Example

Different compositions containing D95 (same as D095) which is a fiberavailable from Schlumberger under the tradename CemNET® and/or Aquazolwhich is a poly-2-ethyl-2-oxazoline available from ISP (InternationalSpecialty Products) were tested. FIG. 1 shows the behavior of differentcompositions:

-   (1) D95-3D 1 mm slot: D95 fiber only, no RWS, the plugging    efficiency was tested on a 3-dimensional slot that had a 1 mm    opening. The plot shows that the filtrate, in other words, the    amount of fluid passed through the 1 mm opening is 430 g.    Accordingly, most, if not all, the fluid was lost.-   (2) D95-3D 2 mmslot: same as above, except that the opening was 2 mm    in width.-   (3) D95-Aquazol-200-3D 1 mm slot: same as test (1), but Aquazol 200,    a RWS, was added the fluid at the concentration of 3 wt %. Aquazol    200 is a poly-2-ethyl-oxazoline polymer, and 200 is the molecular    weight of this polymer corresponding to 200 kDa. The 3D 1 mm slot,    again, means the test was conducted on a 3D slot with 1 mm of    opening. The result showed a significant improvement on reducing the    amount of filtrate passing through the 1 mm slot (˜50 g)-   (4) D95-Aquazol-200-3D 1 mmslot: same as (3), except that the width    of the opening was 2 mm.-   (5) D95-Aquazol-500-3D 1 mm slot: same as (3), the 500 means the    molecular weight of this Aquazol is around 500 kDa.-   (6) D95-Aquazol-500-3D 2 mmslot: same as (5), but tested on 2 mm    opening.

The results for test (3) to (6) showed significant reduction of filtratethat passed through the opening of the 3D slot. It is apparent that theaddition of Aquazole as a RWS material allows a phase separation abovethreshold temperature followed by an increase in the solid content and asticking of the fibers together was observed.

In fact, the inventors surprisingly observed that the incorporation of5% Aquazol (poly-oxazoline) into a 12 ppb (34.26 g/L) WBM with 4 ppb(11.42 g/L) of fibers demonstrates the improved efficiency in terms ofplugging the fluid loss cell, which is defined by the amount of filtratecollected. Whereas, without Aquazol, fibers along did not provide anyfluid loss control (430 ml of filtrate indicates total loss).

1. A composition for use in a well, comprising fibers and a materialable to exhibit reverse solubility, wherein the material comprisespoly(oxy)alkylene or poly-oxazoline and mixtures thereof, and whereinthe material is at least 1% soluble in water at 20° C. and has a cloudpoint that is higher than 20° C. and lower than 60° C.,.
 2. Thecomposition of claim 1, further comprising a second material able tostick fibers in a network when activated.
 3. The composition of claim 2,wherein the second material is embodied as a coating on a part of thefibers.
 4. The composition of claim 1, wherein the fibers comprise oneor more members selected from the group consisting of metallic amorphousfiber, metallic non-amorphous fiber, glass fiber, carbon fiber andpolymeric fiber.
 5. The composition of claim 1, further comprising anaqueous base fluid.
 6. The composition of claim 1, further comprising ahydraulic cement.
 7. The composition of claim 1, further comprising anon-aqueous base fluid.
 8. The composition of claim 1, wherein thematerial is used at a concentration of from 2 to 10 wt %.
 9. Thecomposition of claim 8, wherein the material is used at a concentrationof from 3 to 6 wt %.